# Motion, Work, Energy, and Power

1. Jan 12, 2005

### sp00ky

Okay well my teacher gave me this sheet where you can prepare for the test that will be the next day. The thing is that the sheet consists of questions but no numbers or anythin' so you just have to figure it out how do approach the problems. I have most of them figured out but there might be a few that might have more than one way to do it and just making sure if there is or not.

1. Caculate the average force supplied by the brakes to stop the roller coaster given its initial velocity and stopping distance. What I think I have to do here to get the answers if there were number are:
V1 =
delta D =
V2 =
This is to find the acceleration, then
Fnet = Fbrakes
= ma

2. In the absence of friction, calculate the maximum velocity of the roller coaster given the height of the first hill.
V1 = 0
h2 = 0
Etotal1 = Etotal2
Eg1 + Ek1 = Eg2 + Ek2
Eg1 + Ek1 = Ek2
gh1 + 1/2 v1^2 = 1/2 v2^2

3. In the absence of friction, calculate the velocity oat any other point along the track given the height of the track.
Etotal1 = Etotal2
gh1 + 1/2v1^2 = 1/2 v2^2

5. Given the actualy maximum velocity of the roller coaster, calculate the energy lost to heay and noise during its descent on the first hill.
Eg - Ek = Ebust
(mgh)-(1/2mv^2) = E2

6. Given the force applied by the chain and pulley system to drag the roller coaster up to the first hill, calculate its efficiency.
%eff = deltaE/W * 100
deltaE = ma (delta D)
w = F * delta D

2. Jan 13, 2005

### HallsofIvy

Staff Emeritus
1. Yes, you need to find the acceleration first. Do you know a formula that relates acceleration to distance?

2. Yes, the initial potential energy will be converted to kinetic energy. Presumably the car is pulled to the top of the first hill and then released so its initial speed is 0.

3. Actually, I would say gh1= gh2+ 1/2 v2^2. h1 is the height of that "first hill" h2 is the height of the given point, v2 the speed there.

5. Yes, the difference between the initial potential energy and the kinetic energy at maximum velocity is the energy lost (Ebust?).

6. Yes, W= F* delta D (delta D is the distance the car is hauled up the first hill) is the work done. delta E is the potential energy given to the car (which would be mgh) so the efficiency, as a percent, is (delta E/W)*100.